U.S. patent number 5,536,380 [Application Number 08/448,129] was granted by the patent office on 1996-07-16 for large area sputter cathode having floating target segments.
This patent grant is currently assigned to Leybold Aktiengesellschaft. Invention is credited to Reiner Hinterschuster, Berthold Ocker.
United States Patent |
5,536,380 |
Ocker , et al. |
July 16, 1996 |
Large area sputter cathode having floating target segments
Abstract
Individual target segments (A-F), are mounted on a mounting
plate by means of locating studs inserted into mounting holes of
elongate or circular cross sections in correspondence with the
change in length caused by the thermal expansion of the target
segments. The segments are retained by screws received in tapped
bones in the studs, which are welded to the target backplates. The
individual segments (A-F) each consist of a target backplate and a
target bonded to the backplate. The perimeter of each backplate
over laps the perimeter of each target segment, this overlap
amounting to 0.05-0.2 mm when molybdenum or titanium is used for
the target backplate and an indium-tin alloy is used for the
sputter target.
Inventors: |
Ocker; Berthold (Hanau,
DE), Hinterschuster; Reiner (Hammersbach,
DE) |
Assignee: |
Leybold Aktiengesellschaft
(Hanau, DE)
|
Family
ID: |
6524365 |
Appl.
No.: |
08/448,129 |
Filed: |
May 23, 1995 |
Foreign Application Priority Data
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|
|
|
Jul 28, 1994 [DE] |
|
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44 26 751.7 |
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Current U.S.
Class: |
204/298.09;
204/298.12; 204/298.23 |
Current CPC
Class: |
C23C
14/3407 (20130101); H01J 37/3435 (20130101); H01J
37/3423 (20130101) |
Current International
Class: |
C23C
14/34 (20060101); H01J 37/32 (20060101); H01J
37/34 (20060101); C23C 014/34 () |
Field of
Search: |
;204/298.09,298.12,298.23,192.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Nam
Attorney, Agent or Firm: Felfe & Lynch
Claims
We claim:
1. A sputtering target assembly comprising
a mounting plate, and
a plurality of target segments mounted on said mounting plate, each
target segment comprising a target backplate and a target portion
bonded to said backplate, each backplate having a peripheral area
which extends beyond the target portion mounted thereon,
said target segments being arranged so that in an unheated state
said backplates are not in contact and in a heated state said
backplates are in contact.
2. A sputtering target assembly as in claim 1 wherein each
backplate is provided with a plurality of locating studs facing
away from the target portion, said mounting plate being provided
with a plurality of locating holes spaced to receive said
studs.
3. A sputtering target assembly as in claim 2 wherein said target
segments are rectangular and are mounted in a rectangular array
having a center and a pair of mutually perpendicular bisectors
passing through said center, said locating holes including at least
one fixation hole of circular cross-section which closely receives
a locating stud so that thermal expansion is possible only in
radial directions extending from said fixation hole.
4. A sputtering target assembly as in claim 3 wherein one of said
bisectors defines a boundary between an adjacent pair of target
buck plates, each said back plate having a fixation hole in
proximity to said center.
5. A sputtering target assembly as in claim 4 wherein said locating
holes further comprise elongate fixation holes parallel and closely
adjacent to said one of said bisectors, said elongate fixation
holes permitting thermal expansion of said segments parallel to
said bisectors.
6. A sputtering target assembly as in claim 4 wherein said locating
holes further comprise elongate fixation holes on the other of said
bisectors.
7. A sputtering target assembly as in claim 3 wherein locating
holes remote from said bisectors have circular cross-sections which
receive said studs with sufficient clearance to permit thermal
expansion in radial directions from said center.
8. A sputtering target assembly as in claim 2 wherein each stud is
provided with a threaded coaxial bore, said assembly further
comprising screws received in respective bores to fix said target
segments to said mounting plate.
9. A sputtering target assembly as in claim 8 wherein said screws
have heads provided with sealing means which contact said mounting
plate.
10. A sputtering target as in claim 1 wherein said target portions
are indium-tin alloy and said backplates are one of molybdenum and
titanium.
11. A sputtering target as in claim 1 wherein said peripheral
surface area extends beyond said target portion by 0.05-0.2 mm.
Description
BACKGROUND OF THE INVENTION
The invention pertains to a heatable plate assembly particularly a
sputter cathode having a plurality of target segments consisting of
target portions bonded to backplates and mounted on a cathode
body.
Cathode devices for use in coating systems are known. These cathode
devices consist essentially of a sputter target, which is rigidly
connected to a target backplate and eroded during the course of the
cathodic atomization process. By means of mounting devices provided
on the target backplate, the target backplate is held in position
together with the sputter target on a mounting plate, which is
designed as a cathode body and which is provided with a cooling
device. The surface areas of conventional substrates to be coated
by the sputtering technique can be as large as 400.times.300
mm.sup.2, which requires that the sputter cathode be of similar
size.
A disadvantage of the known sputtering systems is that, when a new
target must be installed after the old sputter target has been used
up, for example, special tools such as lifters are required.
Another disadvantage is that in some cases the sputter target
cannot be replaced by a single person. In addition, large sputter
targets, although desirable in themselves, suffer from the
disadvantage that, during the sputtering process, the sputter
target and the target backplate are heated by the energy from the
plasma in the form of radiation and by the kinetic energy released
by the ions which have been accelerated onto the target. The
sputter target therefore expands as a function of the heat
transferred from the target backplate to the cathode body and as a
function of the design of the cooling device provided in the
cathode body. As a result of this heating, both the sputter target
itself and the target backplate (cathode body) expand. Because the
sputter target is normally bonded to the cathode body, the sputter
target and the target backplate must be made of metals with the
same or similar coefficients of thermal expansion to prevent
differences in the extent to which they change in length or area,
as illustrated by the behavior of a bimetal strip. This sharply
limits the choice of materials.
SUMMARY OF THE INVENTION
The invention simplifies the replacement of the sputter target and
eliminates the limitation on the range of materials available for
the sputter target and the target backplate.
According to the invention the sputter target is built up of
individual segments, each individual segment consisting of a target
portion and a backplate which is bonded to the target portion. In
the unheated state, the individual segments are assembled onto a
mounting plate to form the overall cathode. In the unheated state,
the individual segments are at a defined, contact-free distance
from one another. During the sputtering process, however, the areas
of the individual segments undergo expansion, and the segments come
into contact with each other along their sides. Because the
perimeter of the target backplate segments is larger than the
perimeter of the sputter target segments, the heated segments come
into contact with each other only along the sides of the target
backplates. Any damage which could occur to the abutting edges of
the sputter target as a result of thermal expansion is therefore
advantageously avoided. Because, furthermore, the overall plate
assembly consists of individual plate segments, no special tools
are required to replace the target. The advantage is therefore
obtained that the target can be replaced even by a single person
working alone.
So that the segments can be mounted, the mounting plate has
through-holes of various sizes. The mounting holes in the area
where the bisectors of the surface of the cathode body intersect
have a circular cross section and their diameter matches the
outside diameter of the locating bolts to be used, as a result of
which the segments mounted by means of these holes are able to
expand essentially only in the radial direction relative to these
holes. The mounting holes provided along the perpendicular
bisectors have a slot-type cross section, the long axes of these
slots extending in the radial direction with respect to the point
where the bisectors intersect. With the holes aligned in this way,
it is possible for thermally induced longitudinal expansions to be
absorbed. The changes in length occurring in the other radial
directions (diagonal directions) are absorbed by the other
through-holes provided in the cathode body, these other
through-holes having a circular cross section, the diameter of
which is the same as the length of the slots.
The individual segments are attached by means of locating studs
with tapped central holes, these studs being permanently attached
to the backplates, preferably by welding. The locating studs fit
into the through-holes in the mounting plate and are held in place
by means of screws received in the tapped holes. After the studs
have been positioned, the screws can be screwed into them from the
rear surface of the mounting plate. A sealing ring is inserted as a
vacuum seal into a groove provided around the circumference of the
contact surface of the head of each screw. This sealing ring brings
about a vacuum-tight seal between the surface of the mounting plate
facing the target segments and the rear surface of the mounting
plate. Because the outside diameter of the locating studs is
smaller than the corresponding through-holes, the target segments
"float" on the mounting plate; that is, the target is supported in
such a way that it is free to move parallel to the surface of the
mounting plate. The advantage is therefore obtained that the
segments which shift around with respect to each other as a result
of thermal expansion are kept essentially free of thermal
stress.
The sputter cathode is preferably an indium-tin alloy, and the
target backplate consists of molybdenum and/or titanium. The
overlap between the target backplate and the sputter target is
advantageously 0.05-0.2 mm, and preferably 0.1 mm. Larger overlaps
are less advantageous, because the target backplate itself could
then be sputtered, which would make it possible for impurities to
be introduced into the coating deposited by the sputter
cathode.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plan view of a mounting plate according to the
invention with indication of the positions of segments A-F;
FIG. 2 is a cross section through two adjacent segments;
FIG. 3 is an enlarged, partial plan view of the central area of the
mounting plate seen in FIG. 1;
FIG. 4 is a cross section through the mounting plate along line
4--4 of FIG. 3; and
FIG. 5 is an inverted cross section through a sputter target with a
backplate in the area of a screw connection, the target being
screwed to the mounting plate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows an essentially square cathode body in the form of a
mounting plate 8 having through-holes 19 in the outer peripheral
edge area, which holes are used to hold mounting plate 8 in place.
By means of the additional through-holes 15', 15", 15'", 24a, 24b,
28a, 28b, 38, 38', 38", 38'", individual segments A-F forming the
overall cathode surface are attached to mounting plate 8.
Individual segments A-F are laid next to each other in such a way
that they form an essentially square overall target surface. For
the mounting of the individual segments, specifically segments B
and E, located in the center, mounting holes 24a, 24b, 28a, 28b,
38, 38'" have different cross sections. Through-holes 28a, 28b,
located in the narrower central area of the overall cathode sputter
target surface, have a circular open cross section (see FIG. 3),
into which a locating stud 20 (see FIG. 5) can be inserted with an
exact fit. These mounting holes 28a, 28b serve as fixation holes,
because, when segments A-F are heated, the relative positions of
segments B and E to cathode body 8 change to only an insignificant
degree in the area around mounting holes 28a, 28b. With increasing
distance from the intersection of bisectors h and v, the surface
expansion of segments A-F increases continuously also. To absorb
this longitudinal increase and the change in position of segments
A-F relative to mounting plate 8, through-holes 24a, 24b are
designed as slots essentially parallel to bisectors h and v. These
slots 24a, 24b are oriented with their long axes parallel to the
direction of expansion of segments A-F. Through-holes 38, 38', 38",
38'" have a circular cross section d (see FIG. 3), the open
diameter of which is essentially the same as the length of the long
axes of slots 24a, 24b. Other holes on axis v and holes such as 15'
adjacent to axis h are elongate, while other holes such as 15, 15",
15'" have circular cross-sections which, like holes 38, 38', 38",
38'", provide clearance around studs 20 as shown FIG. 5.
Segments A-F to be attached to mounting plate 8 consist essentially
of two layers, namely, as illustrated in FIG. 2, a target backplate
10a, 10b and a target 12a, 12b, bonded to target backplate 10a,
10b. The target can be made of an indium-tin alloy, for example,
and the target backplate can be made of titanium or molybdenum.
Target backplate 10a, 10b, overlaps sputter cathode 12a, 12b along
the a peripheral area sides by 33a, 33b area of width a, as a
result of which, when segments A-F undergo longitudinal expansion
under the effects of heat, only backplate side surfaces 17a, 17b
are able to press against each other.
To mount segments A-F, locating bolts 20 are permanently attached
by welds 31 to target backplate 10, 10a (see FIG. 5). Backplate 10
is positioned in such a way on mounting plate 8 that locating studs
20 project into the corresponding mounting holes 38 (see FIG. 4),
these segments being detachably connected to mounting plate 8 by
means of screws 22, which are screwed into locating studs 20. To
seal off the vacuum pressure prevailing on the side where the
surface of the sputter cathode is against the atmospheric pressure
prevailing on the rear surface of the mounting plate, a peripheral
groove 30 is provided in head 23 of the screw, into which groove a
sealing ring 18 is inserted. When screw 22 is tightened, the head
comes to rest by way of this ring on mounting plate 8 to form a
vacuum-tight seal. The effective open diameter of mounting hole 38
is, both in the area of screw head 23 and also in the area of
locating bolt 20, designed in such a way that target backplate 10,
with the sputter target 12 attached to it, is able to slide by a
distance c either in only one direction or in any of the directions
in two dimensions allowed by through-holes 38, 38', 38", . . .
* * * * *